Lab 1: Rates of Reaction -- Marble Chips and HCl

In this experiment, marble chips, or Calcium Carbonate (CaCO3), will be dropped into a flask containing Hydrochloric Acid (HCl). The reaction is:CaCO3(s) + 2HCl(l) --> CaCl2(aq) + H2O(l) + CO2(g)The experiment will determine whether or not stirring quickens the reaction rate, which will be illustrated by the slope of the lines in the graphsIf heat and stirring is added to a reaction, then the gas willbe released quicker. This is so because when two compounds interact, or collide, a reaction occurs. If the compounds are made to collide faster, by way of stirring, then the reaction as a whole will start faster and come to completion faster. MaterialsStand with 2 clampsStopwatchGas collection tubeRubber stopperMagnet and Hot plateProcedure1. Set up apparatus:

I)Filled sink with waterII)Set up stand on edge of sink; clamped the gas collection tube with the bottom of tube in the water; made sure that air did not get into tube prematurelyIII)Put stopwatch in clamp near tube which allowed for easy viewingIV)Attached tubing to flask and under the glass collection tube

2. Pour HCl carefully into flask; it did not matter how much was poured in because the HCl was the excess reagent 3. Set up a table for recordings every 15 seconds4. Dropped about 2g of marble chips (CaCO3) into the flask and quickly put the stopper on top of the flask

5. Recorded the amount of gas in the tube at the prearranged intervals6. For part II; repeated steps 1-3, but also added a magnet into flask and put flask on a heat plate. Did not turn on heat, but did turn on stirrer. 7. Dropped 2g of CaCO3 into flask and quickly put the stopper over flask.

Time (minutes)

Volume of CO2 (mL)

0 seconds ---> 1:35 minutes

0

64.0

For Graph, see attachment below, "Gas Collected."

Raw Data, With Stirring

Time (Minutes)

Volume of CO2 (mL)

0:00

0.0

0:15

0.0

0:30

0.0

0:45

0.1

1:00

5.0

1:15

15.2

1:30

25.8

1:45

34.3

2:00

44.3

2:15

53.2

2:30

62.3

2:45

70.5

3:00

80.1

3:15

87.9

3:30

94.3

3:45

100

For Graph, see attachment below "Graph 2"

AnalysisThe first test, in which there was no stirring involved, started to react 1:35 minutes after the CaCO3 was dropped into the HCl. At that time the first bubble of CO2(g) appeared in the gas collection tube. The reaction gave off CO2 at an average rate of:y = 0.02x2 + 0.75x - 4.5Therefore the rate of this reaction is 0.02 M/L/s. The intial rate, however is roughly 1.66 M/L/s. This shows that overall, this reaction is fastest when the gas is first released.The second test, on the other hand, stirred the marble chips. This reaction only took 45 seconds, which is 50 seconds faster then the first test, to release CO2. This reaction released CO2 at an average rate of:y = 0.21x2 + 4.0752x - 12.218given off, creating a slow rate.The average rate of this reaction is 0.21 M/L/s. The intial reaction rate is 10 M/L/s. This data shows that when the molecules are forced to collide into each other more often and with more force (in this case because of the stirring), the reaction will take less time to start, will come to completion faster, and will react at a faster rate.

ConclusionThe first test was a base from which to measure the change in rate during the stirring test. The first reaction occured slowly, for the majority of the molecules in the marble chips are not on the surface. For this reason, only a limited number of actual molecules could react with the HCl. This caused the reaction to take a longer time to get its "ball" rolling. When the magnet was introduced into the flask, and the stirring was set to full force, the reaction started much faster. This is because the magnet would chip off small pieces of the marble, allowing more molecules to react with the HCl, therefore the rate of the reaction is quicker and starts sooner. This experiment is Collision Theory at work. Collision theory states that in order for a reaction to occur, the compounds of the reaction must collide. This is illustrated in the first one, because the marble chips just sat in the HCl and there was not much movement of the molecules. When the marble chips were stirred, however, and got to moving, the reaction occured much faster. If it were safe and possible to heat the HCl, the reaction would occur even faster, for the HCl molecules would be moving so fast and would hit the marble chips with an amazing amount of force (relatively speaking). All this data properly supports the hypothesis, which was when stirring is applied to a reaction, the rate of said reaction will speed up noticably. In this case, it the average rate doubled.

EvaluationOverall, the experiment was well designed and carried out. I could not use a computer to calculate the initial rate. This forced me to estimate the initial rate, and my work is shown in the Paint docs "Initial rate" and "initial rate 2." Discounting percentage error, the experiment properly illustrated collision theory, which was the main goal throughout the experiment.

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